How to check how many queryClient instances are created?

When using React Query, managing and tracking the number of QueryClient instances is essential, especially in large applications, as ensuring unnecessary instances are not created helps prevent performance issues and resource wastage.

How to Check QueryClient Instance Count

React Query itself does not directly provide a function to check how many QueryClient instances have been created. However, there are several ways to indirectly obtain this information:

1. Tracking via Global Variables: In your application, create a global variable to track the number of QueryClient instances. Update this variable each time a new instance is created.

javascript
// Create a global variable
window.queryClientCount = 0;

function createQueryClient() {
  window.queryClientCount += 1;
  return new QueryClient();
}

// Each call to createQueryClient increments queryClientCount
const queryClient = createQueryClient();

1. Using Factory Functions: Create a factory function to generate QueryClient instances and track the count within this function. This approach also facilitates centralized management of QueryClient configurations.

javascript
let clientCount = 0;

function createQueryClient() {
  clientCount++;
  const client = new QueryClient();
  console.log(`Created QueryClient #${clientCount}`);
  return client;
}

const queryClient1 = createQueryClient(); // Output: Created QueryClient #1
const queryClient2 = createQueryClient(); // Output: Created QueryClient #2

1. Encapsulating Components or Context: If using React, encapsulate the QueryClient within a React Context and increment a counter each time it is created.

javascript
import { createContext, useContext, useState } from 'react';
import { QueryClient, QueryClientProvider } from 'react-query';

const QueryClientContext = createContext();

function QueryClientProviderWithCounter({ children }) {
  const [count, setCount] = useState(0);
  const createClient = () => {
    setCount((prev) => prev + 1);
    return new QueryClient();
  };

  return (
    <QueryClientContext.Provider value={{ createClient, count }}>
      <QueryClientProvider client={createClient()}>
        {children}
      </QueryClientProvider>
    </QueryClientContext.Provider>
  );
}

// Use this component for wrapping

Summary

Although React Query does not provide a direct method to track the number of QueryClient instances, simple strategies and code implementations allow effective monitoring and control of their creation. This is particularly important in large-scale application development, as it helps developers avoid performance issues and other complex errors.